1186 PROTEIDS. 



quantities in the stomach and intestine, to judge from the re- 

 sults of artificial digestion, a very small quantity only can be 

 found in the contents of these organs. They are probably ab- 

 sorbed as soon as formed. 



It is now generally considered that the peptones are products 

 of the hydrolytic decomposition of the proteids from which they 

 are formed. This view is based partly upon general considera- 

 tions as to the probable nature of the change from observations 

 of the conditions under which they are formed, and which are 

 known to be hydrolytic in other cases, e.g. the conversion of 

 starch into sugar by the action of enzymes and acids. The one 

 important fact in connection with the relationship of the pep- 

 tones to the mother proteids is that they are, as already stated, 

 products of the decomposition of the latter and of smaller mole- 

 cular weight, an assumption which is warranted not only by 

 the whole tendency of recent investigation and of actual cryo- 

 scopic determinations but more especially by the fact that 

 whereas ordinary proteids are non-diffusible, peptones, and to a 

 less degree the albumoses, are diffusible. 



It was at one time stated that when peptones are injected 

 into the blood-vessels, the blood speedily loses its power of 

 clotting after removal from the body. This action is now 

 known to be due to the albumoses with which the peptones were 

 mixed. The clotting may similarly be prevented by the injec- 

 tion of a 1 p.c. NaCl extract of the pharynx and gullet of the 

 leech : the cause of this has not as yet been fully worked out. 



During the pancreatic digestion of proteids some by-product makes 

 its appearance which gives a characteristic violet or pink coloration 

 on the addition of bromine, or of chlorine in the presence of acetic 

 acid. The substance to which the colour is due has been called 

 tryptophan. 



CLASS VII. Lardacein, or the so-called amyloid substance. 



The substance, to which the above name is applied, is found 

 as a pathological deposit in the spleen and liver, also in numer- 

 ous other organs, such as the blood-vessels, kidneys, lungs, etc. 



It is insoluble in water, dilute acids and alkalis, and neutral 

 saline solutions. 



In percentage composition it is almost identical with other 

 proteids. 



The sulphur in this body exists in the oxidized state, for 

 boiling with caustic potash gives no sulphide of the alkali. 

 The above results of analysis would lead at once to the ranking 

 of lardacein as a proteid, and this is strongly supported by other 

 facts. Strong hydrochloric acid converts it into acid-albumin, 

 and caustic alkalis into alkali-albumin. When boiled with 

 dilute sulphuric acid it yields leucine and tyrosine; by pro- 



