54 PHYSIOLOGY OF FARM ANIMALS [CH. 



and greenish-brown in colonr. In the sheep they are small solid 

 balls, black or dark green. In the pig the faeces are generally 

 semi-solid and human-like with a variable colour and very dis- 

 agreeable smell. In the dog the}^ are very variable, being often 

 gray owing to the presence of lime salts (due to eating bones) and 

 dense in consistency. 



As to the amounts of faecal matter passed, the ox averages 

 a very large amount, as much as 75 lbs. a day, the horse 

 passes 30 lbs. a day (the maximal amount being over 70 lbs. 

 a day), the sheep about 4 lbs. and the pig approximately the same. 

 The quantity passed relatively to the amount of food is less in 

 the carnivora. 



Defaecation is usually in animals a reflex act due to the 

 presence of faeces in the rectum. It is brought about by the 

 rectal muscles assisted by the muscles of the abdomen, though 

 these are not essential since horses can defaecate while trotting. 

 The centre for defaecation is in the lower part of the spinal cord. 

 The sphincter of the anus is relaxed during the process. It 

 contains striated muscles, showing that defaecation may be partly 

 a voluntary process. 



The volume of the stomach and that of the rest of the ali- 

 mentary canal in the different animals, according to Colin, are as 

 follows : 



These results are in general agreement with the statements of 

 mare recent authorities. 



In addition to the movements of the alimentary canal already 

 referred to (such as swallowing, defaecation, etc.) we find that in 

 the presence of food peristaltic waves of contraction are con- 

 tinually passing down the intestine and urging forward the masses 

 of food . Peristalsis of a weaker character in which the constriction 

 of the alimentary tube is very incomplete, also takes jolace, and 

 this serves to propel the outer layer of food and so brings a new 

 supjDly into contact with the gut wall. The walls of the stomach 

 (and in ruminants the proventriculus or rinnen) undergo con- 

 tractile movements which set up surface currents involving the 



