PROTEINS 



75 



of the hydroxyphenyl group, but gives no other protein test. The aro- 

 matic groups present in tyrosine, phenylalanine, and tryptophane cause 

 proteins to yield a positive xanthoproteic reaction. In severe cases of 

 typhoid fever and smallpox, in acute yellow atrophy of the liver, and in 



FIG. 24. FISCHER APPARATUS. 



Reproduced from a photograph made by Prof. E. T. Reichert, of the University of Penn- 

 sylvania. The negative was furnished by Dr. T. B. Osborne, of New Haven, Conn. 



A, Tank into which freezing mixture is pumped and from which it flows through the 

 condenser, B\ C, flask from which the esters are distilled, the distillate being collected in D; 

 E, a Dewar flask containing liquid air serving as a cooler for condensing tube F; G and G', 

 tubes leading to the Geryck pump by which the vacuum is maintained; /, tube leading to a 

 McLeod gauge (not shown in figure); /, a bath containing freezing mixture in which the 

 receiver D is immersed; K, a bath of water during the first part of the distillation and of 

 oil during the last part of the process; 1-5, stop cocks which permit the cutting out of 

 different parts of the apparatus as the procedure demands. 



acute phosphorus poisoning, tyrosine has been found in the urine. 

 Tyrosine crystals are shown in Fig. 25, page 76. 



Cystine, C6Hi 2 04N2S2- Friedmann has shown cystine to be 

 a-diamino-fi-dithiolactyl acid and to possess the following structural 

 formula : 



