46 



MANUAL OF HISTOLOGY. 



and not rarely a number of segments of small spheres rest with their flat 

 side upon a larger globe (d ef). 



Leucin globules may be either unmarked (in which ease they slightly 

 resemble fat-globules), or they may present a concentrically laminated 

 appearance (g g g g). They are frequently met with also with rough 

 surfaces, as though eroded. 



Leucin has no action upon vegetable colours, is quite soluble in water, 

 hydrochloric acid, and alkalies, and slightly so in cold alcohol, while in 

 ether it is insoluble. It may be volatilised by a cautious elevation of 

 temperature. Rapidly heated, it fuses with decomposition. From its 

 solutions it is not precipitated by most of the usual reagents. 



In regard to the occurrence and significance of this substance in the 

 human system, we must distinguish between leucin produced by the 

 putrefaction of histogenic substances, and that formed physiologically in 

 the living body. 



The latter appears often, but not invariably, accompanied by tyrosin 

 as a constituent of many organic fluids and gland juices, in greater or 

 less quantity. Under diseased conditions it is often unusually abundant 



in organs in which traces 

 alone are to be found during 

 health, as for instance in the 

 liver. 



It is present in the spleen, 

 the pancreas, and its secre- 

 tions, the salivary glands and 

 saliva; in the lymphatic glands, 

 the thymus and thyroid glands, 

 and in the fluid saturating 

 pulmonary tissue. In the 

 healthy liver it is not to be 

 found, or only so in traces, as 

 is also the case with the 

 brain. Muscle appears like- 

 wise to be destitute of leucin, 

 though in the heart it may 

 not unfrequently be found as a 

 pathological product. It is at 

 times present in large amount 

 in the kidneys, and may pass 

 into the urine (Staedeler). 

 These facts are of some physiological worth, in that they pr.ove the 

 existence in different organs of distinct series of mutations among their 

 histogenic substances. Thus, leucin is no mutation product of muscle, 

 but of many glandular structures. There can be no doubt, further, that 

 as artificially, so also in the system naturally, does leucin spring from 

 protein compounds, gelatin-yielding substances and elastin ; its physio- 

 logical origin from albuminates by the action of one of the ferments 

 existing in the pancreatic juice has also been proved (Kuhne). 



Leucin is partially excreted with the glandular secretions, and appears 

 in the intestinal canal, and probably undergoes further decomposition 

 also in the body. It is a fact worthy of notice, that in the lymphatic and 

 blood-vascular glands, there occurs besides leucin ammonia also, allowing 

 of the hypothesis that leucin may be resolved there into ammonia and 



Fig. 28. Spheroidal crystalline masses of leucin. a, a very 

 minute simple spherule; b, hemispheroidal masses; c c, 

 aggregates of small globules; d, a large globule sup- 

 porting two halves; e /, a large spheroid of leucin 

 richly studded with minute segments ', g g g g, lamin- 

 ated globules of leucin, some with smooth, some with 

 rough surface, and of very various sizes. 



