Resorption of albuminoid fluids 117 



the greatest distinctness. The inefficacy of the unheated serum must 

 therefore depend on the toxic action of the guinea-pig's macrocytase, 

 because it is this substance alone that can have been destroyed by the 

 heating process. Now, in order that this macrocytase may act, the 

 presence of the fixative is necessary, which leads us to the conclusion 

 that the serum of the guinea-pigs injected by MetalnikofF contained 

 no antifixative. This hypothesis was fully confirmed by experiment. 

 Metalnikoff introduced a drop of guinea-pig's serum into a mixture of 

 aiitispermotoxic serum, heated to 56 C., with spermotoxic serum. 

 The spermatozoa continued their movements in normal fashion. But 

 when afterwards he added a few drops of unheated serum from a 

 normal guinea-pig the motions of the spermatozoa were arrested 

 almost instantaneously. Consequently there was present in the mix- 

 ture rabbit's macrocytase which had been neutralised by the anticytase 

 of the prepared guinea-pig's serum and for that reason the spermatozoa 

 remained motile. But in the same mixture we had also the specific [125] 

 fixative, coming from the rabbit's spermotoxic serum, which remained 

 free and not neutralised. The motile spermatozoa had become im- 

 pregnated with this fixative and a little guinea-pig's macrocytase 

 (against which the auticytase was powerless) was sufficient to make 

 them suddenly cease their movements. 



There is no doubt, then, that the serum of guinea-pigs that have 

 been treated with spermotoxin contains anticytase only and no, 

 or almost no, antifixative. Such is not the case with the antispermo- 

 toxin obtained by us in rabbits that were treated with spermotoxic 

 toxin of guinea-pigs. Several consecutive injections were sufficient to 

 render the serum of the rabbits so treated capable of preventing the 

 action of the spermotoxic serum of the guinea-pig on the motility of 

 the rabbit's spermatozoa. In the mixture of antispermotoxic serum 

 and spermotoxic serum these spermatozoa continue to move for a 

 considerable time, whilst in the control mixture prepared with normal 

 rabbit's serum and spermotoxic serum they become motionless at the 

 end of a few minutes. To obtain this marked effect it was not 

 necessary to heat the antispermotoxic serum as in MetalnikofFs case. 

 Indeed I have performed almost all my experiments with fresh serums, 

 unheated. As the rabbit's serum contains macrocytase capable of 

 rendering the spermatozoa, sensibilised by the fixative, motionless 

 and as this macrocytase cannot be neutralised by the anticytase that 

 is active against the guinea-pig's macrocytase, the fact I have just 

 pointed out indicates that the antispermotoxic serum of my rabbits 



