342 Dr. J. W. Pickering. The Chemical and Physiological 



dogs, it is found not to induce intravascular coagulation, although its 

 chemical and physical characteristics are apparently unchanged. 

 This result shows that the chemica] reactions used for " testing " 

 proteids are not sufficiently delicate to indicate the chemical changes 

 which are demonstrable by physiological methods. The following 

 experiment illustrates this result : 



Experiment 6. Black rabbit (weight 7 Ibs. 9 oz=?.) ; anaesthetic, 

 chloroform and ether ; 120 c.c. of redissolved solution injected pro- 

 duced dyspnoea, exophthalmos, dilatation of pupils. A further injec- 

 tion of 10 c.c. of this substance was immediately fatal. Post-mortem 

 examination failed to reveal any clots in the animal's vessels. Blood 

 withdrawn from the carotids during the injection showed only one 

 minute's decrease in the time taken to complete coagulation. 



Experiment 7. In another experiment, where minute quantities of 

 this substance were very slowly injected, there was no retardation of 

 the time of coagulation, like that produced by the original substance 

 or by a nucleo-proteid. 



Colloid p. This substance is formed by heating together tyrosine. 

 biuret, and phosphorus pentachloride in the ratio of equal weights of 

 the two former substances, with twice the weight of the latter, for six 

 hours at 125 to 130 C. in sealed tubes. The product of this reaction 

 is a grey powder insoluble in cold water, and very sparingly soluble 

 on heating. This substance gives the xantho-proteic and Frohde's 

 reaction, but fails to give typical colour reactions with the other re- 

 agents commonly used in testing proteids. It should be repeatedly 

 washed until all traces of the contaminating phosphoric acid are 

 removed, and then dried in vacua at about 30 C. It readily dis- 

 solves in concentrated ammonium hydrate, and the solution is 

 opalescent and laevorotatory (a D = 48), and in appearance indis- 

 tinguishable from that of the other colloids produced. It gives the 

 following distinctive reactions as classified in the annexed table, but 

 does not digest when subjected to the action of either pepsin and 

 0'2 per cent, hydrochloric acid for three days at 38 C., or of an 

 alkaline solution of trypsin, kept at the same temperature for a 

 similar time. It yields the following distinctive reactions: 



Colloid 3. 



