94 ANIMAL BASES. 



ginally contained has been expelled by pressure. When thus 

 treated it may be kept a considerable time, during which it is 

 slowly undergoing an alteration, which renders it more agree- 

 able to the taste. If the liquid portion has not been squeezed out 

 with care, it undergoes a species of putrefaction, similar to what 

 takes place when moist gluten of wheat is left in a similar state. 

 Proust conceived that during this process a peculiar acid was 

 formed, which he distinguished by the name of caseic acid, toge- 

 ther with another substance which he called caseous or cheesy 

 oxide. Braconnot showed that the caseic acid of Proust was com- 

 posed of a congeries of substances which he separated from each 

 other. The cheesy oxide he found a peculiar substance, and dis- 

 tinguished it, as has been already stated, by the name of apose- 

 pedin. 



He mixed 4167 grains of fresh cheese from creamed milk 

 with 61 cubic inches of water, and left the mixture to putrefy for 

 a month in a temperature varying from 68 to 77. During this 

 interval the greatest part of the cheese was dissolved. The so- 

 lution was separated by filtrations from the undissolved portions. 

 Its smell was putrid, but no odour of sulphur could be distin- 

 guished in it. When evaporated to the consistence of honey it 

 gradually congealed into a granular mass, one portion of which 

 dissolved in alcohol, while another portion remained unattached 

 by that liquid. The first of these portions was the caseate of am- 

 monia of Proust, and the second his caseous oxide. 



This last substance was dissolved in water and the solution 

 treated with animal charcoal, which rendered it colourless. This 

 liquid being left to spontaneous evaporation, deposited brilliant 

 crystalline vegetations, constituting rings and cauliflower-looking 

 concretions on the edges of the liquid. To obtain it perfectly 

 white it was necessary to dissolve and evaporate it two or three 

 times successively. Thus purified its properties were as follows : 



Its colour is white ; it has no smell, its taste slightly bitter" 

 with a flavour of roasted meat It crackles under the teeth ; it 

 is heavier than water, and is easily reduced to powder. It burns 

 away without leaving any residue. When heated in a tube of 

 glass open at both ends a portion of it is volatilized unaltered, 

 under the form of long slender crystals. Every time that this 

 process is repeated a new portion is decomposed. When dis- 

 tilled per se in a retort it does not sublime but undergoes decom- 

 position. A solid oil passes over into the receiver together with 



