136 



Part lit. — SideerUh Annual Report 



Protoplasm. 



One must distinguish the small amount of protoplasm in the prini 

 ordial egg from the larger amount of nutritive yolk present in the egg 

 at later stages. The former is the formative or germinal protoplasm, 

 the latter the nutritive yolk. One must not, however, forget that the 

 latter is not to be regarded as simply nutriment to be burned up, 

 but building material which, by gradual transformation, is changed into 

 the formative protoplasm ; or, rather, some of its constituents pass from 

 the nutritive yolk to the germinal protoplasm. In it are present the 

 forerunners of the organised substance of the germinal protoplasm. The 

 interchanges in the ovum during growth take place between nutritive 

 and formative protoplasm, and then between the latter and the nucleus. 

 The specific gravity of the nutritive yolk and formative protoplasm varies. 

 In some cases the latter is of lower specific gravity, so that the nutritive 

 yolk takes the lower position when the germinal disc is formed. In 

 many cases, however, the germinal disc is of higher specific gravity, as 

 in the ova of the marine Teleosteans, where it is situated, along with the 

 micropyle, at the lower pole. Before the germinal protoplasm is collected 

 into one mass, to form the germinal disc, it may be seen in many ova 

 as a fairly well-marked zone around the vitellus, in the outer part of the 

 egg. This is very well seen in the ovum of the cod. 



The consistence of the yolk alters in different ova, from solid yolk- 

 plates in the cyprinoids to a fluid of a watery nature in the teleostean 

 ova. Both are, however, of essentially the same chemical composition. 

 If you add to the vitelline fluid of the salmon ovum acetic acid, you at 

 once get a precipitate of a flocculent type, easily soluble in excess of the 

 re-agent. This precipitate contains phosphorus organically bound. On 

 pouring the vitelline fluid into distilled water, a precipitate of the same 

 nature is obtained. It is a nucleo-alburain, containing in it a body 

 only with difficulty attacked by the peptic ferment of the gastric juice. 

 This body is attached to the albumin. It has been carefully studied in the 

 case of the vitellus of the hen's egg. It is a paranuclein, that is to say, 

 a body similar in some of its characters to the true nucleins which occur 

 in the nuclei of some cells, e.g.^ pus cells. It contains phosphorus 

 organically bound, and is only slowly attacked by pepsin, like the true 

 nucleins ; but, unlike those, it does not furnish nuclein bases on decom- 

 position with acids. The yolk-plates, which have been described so 

 frequently as occurring in difl'erent fish and amphibian ova, were at first 

 regarded as composed of fat. Johannes Miiller, in 1842, said that these 

 plates were soluble in boiling alcohol and ether, leading him thus to 

 believe that they were of a fatty nature. Virchow, however, in 1 850, 

 showed that, in addition to fat, they contained a substance which gave 

 proteid reactions. In 1854 Valenciennes and Fremy cleared up the 

 subject much more than the previous writers. They separated the plates 

 in a pure condition, and showed that they were of a proteid nature, but 

 thought that they difi'ered from the ordinary albuminous substances by 

 giving no violet colour with hydrochloric acid. A point of far greater 

 importance was that they were found to contain phosphorus in com- 

 paratively large quantity, and organically bound. From the yolk-plates 

 of different varieties of ova they obtained proteid substances, which 

 differed in slight particulars from one another, and so they gave several 

 names to these, e.g.^ ichthin, ichthidin, emydin. These substances are of 

 the greatest importance physiologically, as being the first of the tissue- 

 forming bodies to be prepared pure. For a long time it was supposed 

 that they owed their phosphorus percentage to an admixture with 



