280 ANIMAL PROTEINS 



well-rotted farmyard manure contains very approximately 

 10-12 Ibs. nitrogen, about the same amount of potash, and 

 about half that quantity of phosphates. It is, however, 

 very variable. Horse manure is rather richer than cow 

 manure, but more liable to loss on storage. Pig manure is 

 intermediate between them. Sheep manure is distinctly 

 richer in protein, and has therefore greater value as nitro- 

 genous fertilizers. Poultry droppings are richer still, 

 perhaps partly because they include the urinary products. 

 When fresh they contain 18-25 Ibs. nitrogen, 12-24 ^s. 

 phosphate, and 6-12 Ibs. potash per ton. When dried they 

 have about double the value. Pigeon manure is even richer, 

 and the pigeon loft scrapings have a manurial value about 

 double that of dry hen manure, and eight times that of 

 farmyard manure. Guano is much decayed droppings of 

 sea birds on the tropical coasts of Africa and America. 

 The supplies are now quite exhausted, and the market 

 guanos are chiefly artificial fertilizers. 



There is one other animal protein which must be referred 

 to before this volume is concluded, viz. silk. This is 

 obtained from the cocoon of the " silkworm," which is 

 the general name given to the larvae of certain bombycid 

 moths. These larvae feed on the leaves of the mulberry, 

 and when ready to pupate produce a considerable supply 

 of a soft and delicate thread which is wound round about the 

 larva itself. This is the raw silk, and it is unwound from 

 the cocoon in a machine called the " silk-reel," and may 

 then be wound into a thread. Two or more threads twisted 

 together form " thrown-silk." Silk threads are also woven 

 into cloth of characteristic texture and appearance. This 

 protein thus forms the raw material of one of the most 

 important textile industries. 



From the fish trade there is much animal protein, which 

 is useless for food purposes and which, to avoid nuisance, it 

 is necessary to convert promptly in fertilizers. During the 

 herring season there is the disposal in this way of the 



