422 SCIENTIFIC RECREATIONS. 



NITROGENOUS SUBSTANCES. 



There are certain albuminous compounds which we must mention here. 

 These are albumen, fibrine, and caseine. Albumen is the white of egg ; 

 fibrine is, when solid, our flesh and muscular fibre, while caseine is the sub- 

 stance of cheese. These are very important compounds, and the albu- 

 minous bodies are of the very highest importance as food, for the solid 

 portion of blood, brain, and flesh consist, in a great measure, of them. 

 Albumen, fibrine, and caseine contain carbon, hydrogen, nitrogen, and oxygen, 

 with sulphur and phosphorus. 



ALBUMEN. The most familiar and the almost pure form of albumen 

 is in the white of eggs, which is albuminate of sodium. It also exists in 

 the serum of the blood, and therefore it is largely found in the animal 

 kingdom. It can also be extracted from seed or other vegetable substances, 

 but it is essentially the same. Albumen is very useful as an antidote to 

 metallic poisons. It forms about 7 per cent, of human blood. It is soluble 

 up to about 140 Fah. ; it then solidifies, and is precipitated in a white 

 mass. Albumen is used in the purification of sugar, etc. 



FIBRINE is found in a liquid condition in blood. The vegetable fibrine 

 (gluten) is prepared by kneading wheat flour in a bag till the washings are 

 no longer whitened. Like albumen it is found both in a solid and liquid 

 state. 



Caseine is seen in the skin which forms upon milk when heated, and 

 forms about 3 per cent, of milk, where it exists in a soluble state, owing to 

 the presence of alkali : but caseine, like albumen, is only soluble in alkaline 

 solutions. As we have said, it is the principal constituent of cheeses. Caseine 

 is precipitated by the lactic acid of milk, which is produced by keeping the 

 milk too warm. Caseine, or curds, as they are called, are thus precipitated. 

 The milk is said to be " sour," or turned. 



MILK, the food of the young of all mammalia, is composed chiefly of 

 water, a peculiar kind of sugar, butter, and caseine. It is this sugar in milk 

 which causes the lactic acid mentioned above. The actual constituents of 

 milk are as follows : 



Water 873*00 



Butter . 30*00 



Sugar 43'9o 



Caseine. 48*20 



Calcium (phosphate) . . 2*31 



Magnesia . . . . . 0*42 



Iron ......... 0*07 



Potassium (chloride) 1*44 



Sodium . . ...... 0*24 



Soda (with caseine) . . . . . . 0*42 



lOOO'OO 



