Tuesday, 11 August 2015

Dorothy Sladden (1907-1937): Ernest W. MacBride, Evolution and Eugenics. Part 2. Frogs’ eggs, sports and monstrosities

As well as for the inheritance of acquired characters, MacBride was also looking for environmental factors that caused mutations, in order, it seems, to provide an explanation for the findings of the Mendelian geneticists. The basis is explained by the opening paragraph of his article, The work of Tornier as affording a possible explanation of the causes of mutations, written in 1924 for Eugenics Review (15, 545-555):

In a previous communication to the Society I gave an outline of recent discoveries which tended to show that the effects of habits acquired during the lifetime of the individual were transmitted to posterity. Since that time more and more evidence pointing in the same direction has come in, and finally the recent experiments of Pavlov may be regarded as decisive on the question. The inheritance of environmental effect is therefore a vera causa, and has probably been the chief, if not the only cause, of the evolution of the plant and animal kingdoms, but it is certainly not the only cause of variation. The conspicuous deviations from the normal, known as sports or monstrosities, which appear suddenly, which are inherited strongly, and which "mendelize" when crossed with the type, still demand an explanation of the cause of their occurrence. It is on characters such as these that the breeder seizes when he wishes to produce a new strain; and it is the offspring of similar "sports" in the human race that fill the slums of our great cities.
     To say that these sports owe their origin to "mutations" in the chromosome-complex of the type is merely playing with the question; it is, in the words of Darwin, to substitute a form of words for an explanation. Granted that if the hereditary potentiality of a stock is changed, the nuclei of the germ cells have undergone a change; to assert this is merely to push the difficulty one step further back. What has changed the nuclei? Till we can answer that question all talk of an explanation of mutations is futile.
     …In view of these facts it occurred to Gustav Tornier [1858-1938; he worked in Berlin] that there must be some general underlying cause for the production of these abnormalities. It seemed to him futile to attribute each one to the separate appearance by chance of a '*factor." He was thus led to formulate what Milewski calls an “epoch-making theory” to the confirmation of which Milewski has himself largely contributed. Like the Mendelian theory itself the Tornierian hypothesis did not at first attract the notice to which it was entitled. This was due to two causes—first because the theory conflicts with all preconceived ideas as to the origin of mutations, and secondly because Tornier has published his results for the most part in journals which have not a sufficiently wide circulation to reach zoologists in general. Tornier's theory is as follows:—Every embryo is endowed at the beginning of its existence with a certain quantity of protoplasmic energy. This energy manifests itself in two ways: (1) by the early beginning and vigorous character of the movements of the embryo; (2) by the ability of the embryo to resist the tendency of all its tissues, especially those of a less active growth, to absorb an excess of water—in a word to regulate the intake of water. In practically all eggs the portion of less active growth is that in which the yolk globules are stored, and hence Tornier speaks rather too loosely of an absorption of water by "the yolk" and its consequent swelling. The swelling is not confined to yolk-containing cells, nor strictly speaking is it the yolk itself which swells, since this consists chiefly of globules of a lecithin-like substance insoluble in water. The very same swelling takes place in mammalian embryos in which there is no yolk. Davenport and Parker showed long ago that a large part of the increase in bulk which embryos undergo during the earlier period of their development is due to the imbibition of water.
     Now according to Tornier, when an embryo is exposed in the earliest period of existence to scarcity of oxygen, the protoplasm becomes weakened and is not able to prevent the overswelling of the less active portions of the body by water. This abnormal swelling— since the embryo is confined within a relatively inextensible membrane—leads to pressure on the actively growing parts which impedes their growth, distorts their shape, and in extreme cases, prevents their growth altogether. If we examine in detail its effects in goldfish embryos we find that all the natural cavities of the body, such as the buccal cavity, the gill cavity (beneath the operculum), and the body cavity become enlarged beyond their natural sizes, whilst strong pressure is exerted by the swollen yolk-sac against the growing embryo in an antero-posterior direction, so as to impede the natural tendency of the embryo to grow in length.
     …The interest in all studies of heredity to the Eugenics Education Society is, of course, their   applicability to human conditions.
     Tornier's work suggests strongly that bad conditions during the period of conception and the early phases of development may be the original cause of the degenerative mutants in man, including under that head not only mental defect, but haemophilia, night-blindness, colour-blindness, &c. But the important fact is that, however caused, the plasma-weakness is handed on to posterity. It is the object of negative eugenics to prevent these plasma-weak stocks from adding their quota to the race, by discouraging their reproduction. In the future we may hope that eugenics, in conjunction with medical research, may perhaps detect and isolate the specific causes of plasma-weakness, and thus diminish, if not entirely prevent, the appearance of plasma-weakness in the race.

It is difficult, when looked at from 2015, to believe that this was written by anything other than a crank. It is also difficult to believe, again when looked at from 2015, that the work in the first two papers, on the development of frog embryos after an environmental insult, were other than fanciful and difficult to not believe that they were thought as fanciful at the time by those not involved directly with MacBride. The introduction to Dorothy Sladden’s first paper summarises the thoughts of Tornier as expressed in MacBride’s article and explains the line of reasoning for the experiments she did:

In 1908, Tornier published a paper on the probable causes of the formation of the abnormal "fancy" races of goldfish. All these races originated in China where the wild ancestor (Carausius [sic] auratus*) still abounds in the streams, It had been supposed that these races were produced by a secret process known only to the Chinese breeders. The fish during winter were kept crowded in earthenware pots, on shelves in dark and insanitary huts; in summer they were transferred to small and filthy tanks overgrown with weeds. In these tanks they spawned and much of the spawn perished; amongst the fraction which survived, however, all sorts of abnormalities were found. By selecting the most striking of these, the breeders secured the parents of their “fancy" breeds, which showed in every succeeding generation a strong tendency to revert to the normal; only by the most rigid selection was anything like a "pure" race obtained.
    Tomier drew the conclusion that, the abnormalities were due to the effects of lack of oxygen in very early stages of development. This lack induced what he called "plasma-weakness" in different parts of the formative area of the very young embryo. In consequence of these localised areas of weakness the protoplasmic part of the egg was liable to mechanical distortion, induced by abnormal pressure from the yolk ; the latter absorbed water and swelled, thus crushing and destroying the protoplasmic structures from which the future organs of the adult arc formed.

The practicalities of the initial experiments involved keeping frog eggs in a 10% sucrose solution for four hours and seeing how the eggs and tadpoles developed. the sucrose solution was used in the belief—as in Tornier’s experiments outlined in MacBride’s article—that it would reduce the concentration of oxygen in the water sufficiently to affect the developing embryo. This is the summary of that paper:

Eggs of Rana temporaria were exposed, at the end of segmentation, 24 hours after fertilisation, to a 10 per cent, solution of sugar in tap-water for 4 hours; they were then transferred to normal aerated water. The resulting larvae exhibited marked structural abnormalities, although these might not be obvious for a prolonged period, e.g., 3 to 4 months after fertilisation. These abnormalities have, been described as (a) distention of body-cavity; (b) rupture of gut and extrusion of yolk; (c) flexure of tail; (d) distortion of sacral region; (e) non-appearance of limb.

However, in the second paper it was realised that the effect of immersion in sucrose was probably caused by an osmotic effect rather than lack of oxygen (I calculate the oxygen concentration in the water would have been reduced by only 9%):

Summarising these somewhat inconclusive results, it would seem that the effect of sugar is not the removal of oxygen as previously assumed, but very possibly osmotic action and is responsible for the early abnormalities in particular, while pH decrease may be responsible for the later ones…It now seems possible, however, that overcrowding may have seriously affected all the previous results.

The experiments show nothing other than when frogs’ eggs are damaged, the tadpoles do not develop normally, although I am sure that MacBride really fancied the notion that dirty conditions lead to ‘mutations’ (as proposed by Tornier for the genesis of the domestic strains of fancy goldfish) which are then embedded forever in the working class unless expunged by negative eugenics, and that is the reason why the newly-graduated Miss Sladden was given the project.

Dorothy Sladden’s skills in rearing frogs through metamorphosis are evident and were obviously put to good use by others in in the department. For example, Peter Gray in a paper on development of the development of the amphibian kidney also published, like her first paper, in 1930, thanks her profusely: ‘indeed, it is to her skill in the rearing of animals under artificial conditions that I am indebted for the greater part of my material.”

The studies described here have nothing of importance that I can see. By contrast the next set of experiments she did produced biologically significant results and should be seen in a different light to those on frogs' eggs. I will deal with them in my next post, Part 3.

The two papers are:

Sladden, D.E. 1930. Experimental distortion of development in amphibian tadpoles. Proceedings of the Royal Society B 106, 318-325

Sladden, D.E. 1932. Experimental distortion of development in amphibian tadpoles. Part II. Proceedings of the Royal Society B 112, 1-12

*She was confusing the name of the goldfish (Carassius auratus) with the organism she wroekd on next, the stick insect (Carausius morosus)