ADAPTATION OF TISSUES AND THEIR PRODUCTS 473 



ible, and moreover, the heteroagglutinins may be toxic for the spermatozoa, 

 whereas the agglutinations caused by homoioagglutinations are reversible and 

 non-toxic for the spermatozoa (Little and Just). In addition, there has been 

 found a more direct specific adaptation between eggs and spermatozoa, inas- 

 much as a smaller number of spermatozoa suffices for the fertilization of eggs 

 of the same species than for that of eggs of other species (Jacques Loeb, 

 R. F. Lillie). 



A specifically adapted substance, which seems to be a protein, has been 

 extracted from the sperm of the giant Keyhole limpet ; it is able to dissolve 

 the membrane of eggs of the same species. Correspondingly Abalone (Haliotis) 

 sperm yields a lysin which acts on the eggs of Abalone ; cross-lysis between 

 limpet and Abalone does not occur (Tyler). In addition sperm extracts of 

 Arbacia seem to agglutinate eggs of the same species, and this egg-agglutinating 

 substance resists boiling for hours. Tyler has found that in certain echinoderms 

 and worms there may occur in a watery extract of egg, a substance, fertilizin, 

 which combines in a specific manner with the homoiogenous sperm, but with- 

 out causing a noticeable agglutination of the spermatozoa. Such fertilizin he 

 calls "univalent." There may be extracted from spermatozoa a similar species- 

 specific substance, an antifertilizin, which combines with the fertilizin, neutral- 

 izes its sperm agglutinating power, and agglutinates the eggs from which the 

 fertilizin can be extracted. Tyler noted moreover a certain relationship between 

 fertilizin and the fourth component of complement which is present in normal 

 guinea pigs serum. Complement is fixed by fertilizin, but is released from 

 this combination by the action of antifertilizin; there exists thus a certain 

 analogy between the action of complement and antifertilizin. 



In a previous chapter we have referred to hormone-like substances which 

 accelerate or induce metamorphosis in insects ; also in amphibia there are indi- 

 cations of the existence of substances accelerating metamorphosis. In a similar 

 way, Caswell Grave prepared from the larvae of two ascidian species, 

 Polyandrocarpa and Phallusia, extracts which induce metamorphosis in their 

 own but not of the other species. These substances are therefore species- 

 specific, yet they are neither proteins nor lipids ; perhaps they are amino-acids ; 

 but their chemical nature has not been established. 



According to F. B. Turck, a substance developing in autolysed muscle, or 

 also in other tissues, has on certain cells very characteristic effects, which are 

 either stimulating or injurious, according to the quantities used. This sub- 

 stance, which Turck names "cytost," seems to be species-specific. Thus, 

 cytost from chicken acts specifically on chicken cells in tissue culture, and 

 human cytost on human cells. Similarly, extract of dried paramaecia appar- 

 ently stimulates the multiplication of paramaecia, while extracts from chicken, 

 rat or human tissues do not have such an effect. Corresponding observations 

 were made with bacteria. In immunization experiments it was shown that 

 injection of autolysed muscle of the cat called forth active immunization 

 only against cytost from the cat, but not against that prepared from other 

 animals. 



Specific adaptation may be found, furthermore, in the case of enzyme 



