Vlll PREFACE. 



human scarlet-fever may be derived from a disease afflicting cows. 

 Indeed, the announcement of this fact and of the facts on which 

 it is founded was received by the scientific world as a revelation 

 of a startling kind, and as one of the greatest importance. 



Those who can understand the advances which have been 

 recently made in science, and in the field of Pathology in 

 particular, cannot but feel rejoiced at the prospect in store 

 for those who will come after us. As each year pursues its 

 course, our knowledge of diseases, of medicines, and of thera- 

 peutic appliances becomes more wide ; and it should not be 

 forgotten that facts and principles derived from the study of 

 maladies as they are manifested by the lower animals, have even 

 already affected the art and science of human medicine and 

 surgery, and must still more importantly influence them in the 

 future. There can be no doubt that, in proportion as micro- 

 scopical methods advance in perfection, we shall learn more 

 and more concerning the relations which subsist betwixt human 

 diseases and those which afflict animals. It is possible we may 

 find that there is a much more far-reaching interaction between 

 those disorders which afflict man and those of the animals which 

 he has domesticated, than we can now form any conception 

 of. If this is so, the clue is certainly one of the utmost value. 



Hence it is obviously very important that the diseases of 

 animals should be well managed, and that the whole subject of 

 sanitary science in relation to animals should be thoroughly 

 attended to. Especially is this necessity manifest, when we 

 consider that plagues of different kinds among animals very 

 frequently break out. It is well known that the ancient records, 

 both of Scriptural and of Pagan history, repeatedly mention 

 the occurrence of epidemics among cattle. We read that in 

 the time of Moses the cattle of Egypt were decimated by 

 the ** murrain," and that all kinds of animals died in con- 



