82 ALBUMINOUS MATTEKS. 



another substance. The action of vegetable diastase in converting 

 starch into dextrine and glucose is a process of this nature ; and it is 

 found that one part of diastase is capable of effecting the transformation 

 of 2000 parts of starch. The albuminous ingredients of the saliva, of 

 the pancreatic and intestinal juices, exert a similar action on hyd rated 

 starch. The whole process of digestion and assimilation is in great 

 part made up of a series of such catalytic changes, in which the 

 nutritious matters undergo their requisite transformations, by contact 

 with special albuminous ingredients of the blood, the tissues, or the 

 secretions. 



At a temperature of 300 (570 F.) or over, the albuminous matters, 

 like other organic substances, are destroyed and decomposed into 

 gaseous products. But if subjected for a certain time to a temperature 

 of about 125 (257 F.) ? they undergo a change in addition to their 

 coagulation, by which a distinct and agreeable flavor is developed, and 

 by which they become suitable for use as human food. It is this change 

 which is produced in the process of cooking, and the peculiar flavor 

 which results always depends upon the presence of a certain quantity 

 of albuminous matter in the substance employed. If the temperature 

 at which the cooking process is carried on be too low, the characteristic 

 flavors are not developed; if it be too high, they are destroyed and 

 replaced by empyreumatic odors, from the combustion or decomposition 

 of the ingredients of the food. 



Lastly, the albuminous matters are distinguished by the property of 

 putrefaction. This is a process by which dead animal substances, 

 when exposed to the atmosphere at a moderately warm temperature, 

 gradually soften and liquefy and are finally decomposed, with the pro- 

 duction of certain fetid and unwholesome gases, among which are 

 hydrogen sulphide and carbide, usually with more or less carbonic acid, 

 nitrogen, and ammoniacal vapors. The mixture of these emanations 

 causes an odor which is easily recognized as a "putrefactive odor;" 

 and wherever such emanations are perceived, it is an indication that 

 some substance containing albuminous matters is undergoing decom- 

 position. As these albuminous matters are more abundant in the 

 tissues and fluids of animals than in those of vegetables, the phenomena 

 of putrefaction are also most distinctly marked in the decay of animal 

 substances. But they will take place in both, under the requisite con- 

 ditions. A solution of nitrogenous vegetable matters will present all 

 the essential characters of putrefaction, though not developed with the 

 same degree of intensity as in fluids of animal origin. 



In order that putrefaction may take place certain special conditions 

 are necessary. In the first place it requires the access of atmospheric 

 air, or of some fluid containing oxygen. If the putrescible substance 

 be first boiled so as to expel all the free oxygen contained in its fluids, 

 and if then, while the boiling is going on, it be inclosed in a hermetically 

 sealed vessel, no putrefaction takes place, but the substance remains 

 unaltered for an indefinite time. It is by this means that cooked meats 



