786 . HEPOET— 1900. 



2 On d Peptic Zymase in Young &nhri/os. 

 By Marcus Hartog, M.A., D.Sc, F.L.S. 



In 189G I comnmnicated to the Association a note in wbicli I referred incident- 

 ally to the discovery of a peptic zymase in the embryo of the frog at a stage when 

 the macromeres appear as a white plug' in the region of the blastopore, in the 

 entire embryo of the chick after twenty-four hours, and in the extravascular 

 blastoderm after three days' incubation. These observations were made by the 

 classic method of killing and coagulating with absolute alcohol, drying and 

 powdering, extracting with glycerine, precipitating with absolute alcohol, and 

 ascertaining the properties of this precipitate on boiled white of egg and 

 boiled blood-fibrin. In successive years I obtained only negative results. A 

 hint from Professor J. Reynolds Green gave me the explanation of these con- 

 tradictory results. In 1896 I had the valuable assistance of Mr. E. J. Butler, 

 and was able to carry through each series of experiments continuously ; while in 

 the three following years they were protracted indefinitely. This spring I was 

 able to confirm my original results, changing my methods to avoid delay and con- 

 sequent loss of zymase. The objects themselves were killed in chloroform- or 

 thymol-water and pounded ; and instead of using other substances for diges- 

 tion' I contented myself with the abundant material of the vitelline granules 

 present in each case within the cell. 



I relied in all cases on the ' biuret test' of Piotrowsky, consisting in warming 

 the product of digestion (after neutralising, boiling, and filtering to remove all acid- 

 albumen) with strong caustic alkali and a trace of copper sulphate; the pink 

 coloration reveals the presence of albumoses or peptones. On some occasions the 

 chick-blastoderm tests turned j-ellowish brown as the temperature continued to 

 rise, and on boiling there was an abundant dark precipitate, indicating the presence of 

 a reducing body. A zymase capable of yielding such a product has recently been 

 described by Miiller, who, however, has only found it active in neutral liquids. 



No trace of any other ferment has been found so far ; it is noteworthy that all 

 observers are agreed in the recognition of a 2wptic ferment only in the holozoic 

 Protista. 



Frog embryos kept in thymol water in a stoppered jar in the dark — in a closed 

 locker — for a month had lost all digestive properties. 



Two important conclusions appear to follow : — 



1. In all plants, so far as is known, it has been shown that the cell cannot 

 directly utiHse the reserves that it contains, but only the products of their hydro- 

 lysis ; and tliis hydrolysis is not a function of the living protoplasm itself, but of 

 the zymases it forms, since the process can be reproduced in vitro working with 

 the killed cell or its extract. It would seem almost certain that the same law 

 holds good for the animal cell. 



2. These facts explain the apparent exception to the law of division at the 

 doubling of the volume formulated by Herbert Spencer, as I indicated in my, 

 note of 1896. A cell that instead of growing by its protoplasm only accumulates 

 reserve material has no need to constantly readjust its surface to its volume. 

 "When, however, the formation of a zymase enables it to utilise its reserves, and 

 its protoplasm grows at the expense of the products of their digestion, the need for 

 augmented surface asserts itself, and we get the repeated cell-divisions so marked 

 in the ' segmentation ' of the embryo and in other cases of brood-formation. It 

 follows also that two distinct processes have been compounded under the single 

 term of 'anabolism:' («) the building up and storage of reserves; (h) the 

 growth of the protoplasm at the expense of nourishment from without, or the 

 digestion of the reserves within. From this point of view the segmentation of the 

 embryo is certainly an anabolic process of the second category, aiid not mainly 

 catabolic, as usually stated. 



