INTRODUCTORY. 3 



material will fill the arteries of the bodj, but the valves 

 of the veins prevent fluid from passing from their larger to 

 their smaller branches, so it is here necessary to com- 

 mence at the smaller vessels. Lymphatics are injected 

 by introducing the point of the syringe into the areolar 

 tissue beside the arteries and veins of an organ, when 

 the mercury will generally find its way to the lym- 

 phatics ; they are, however, but seldom dissected, and 

 being valvular like the veins, cannot be injected from the 

 larger vessels. 



Solutions of nitric and other acids and alcohol are used 

 for hardening the softer organs, as the brain and the 

 eye, while by maceration or boiling the bones may be 

 cleaned, and thus rendered fit for demonstration of their 

 peculiarities ; by boiling also we render apparent the 

 arrangement of the muscular fasciculi of the heart. The 

 age of the subject influences its value for dissecting 

 purposes. Young animals, in consequence of the tender- 

 ness of their areolar tissue, do not present that similarity 

 between bands of white fibrous tissue and the nerves 

 which we find in the older subject. They also present 

 well-marked separations between the bones, and in many 

 cases the various ossific centres from which these bones 

 originate ; the muscles, though more easily separable, are 

 less marked and more liable to tear ; an older subject is, 

 therefore, preferable for dissection of muscles. Fat sub- 

 jects are said to keep better than lean, but this advantage 

 is more than counterbalanced by the difficulty of removal 

 of the adipose tissue from some parts. Coarse lymphatic 

 animals present bulky but soft muscles, while well-bred 

 horses and asses afford firm well-defined muscles. Since 

 also they occupy less space and are less expensive, asses are 

 generally dissected by the veterinary student. They do 

 not difler essentially in structure from the horse. The 

 value of an animal for dissection may, after death, be 

 judged by taking into consideration the period before 

 accession of rigor mortis or death stiffening and the length 

 of its duration. When death has ensued from nervous 

 prostration the vital powers soon lose their control over the 

 tissues. Coagulation of the albuminoid matter in the 

 muscles occurs, constituting rigor mortis, but soon decom- 

 position commences as a result of the substitution of 

 chemical for vital force in the tissues. Such a subject, 



