MICROSCOPE IN-DOORS. 71 



semble those found on the surface of the skin. 

 Cells of a different kind line the air-passages. If 

 a snip be taken from inside the nostril of a recently 

 killed ox or sheep, it will be found to be composed 

 of cells which are fringed with cilia at the top 

 (Fig. 5, PL 1). These cilia are constantly moving, 

 and produce the motion of the mucus on the sur- 

 face of these passages which is essential to their 

 healthy action. 



The blood of animals presents us with objects of 

 high interest. The human blood consists of a 

 liquid in which float two kinds of cells. They 

 are discoid bodies, from the one three thousandth 

 to the three thousand five hundredth of an inch in 

 diameter ($353 to 3^5) (Fig. 6, PL 1). They are of two 

 sorts, pale and red ; the latter are rather smaller, 

 but are by far the most abundant. They present 

 a little spot in the centre, which is called a nucleus , 

 and this again another little spot, which is called 

 a nucleolus. The red globules vary much in size 

 and form in different animals. Thus, in birds, 

 reptiles, and fishes, they are oval instead of round ; 

 and, mostly, in these three classes much larger than 

 in mammals. This is especially the case in the 

 batrachian reptiles, to which the frog and toad 

 belong (Fig. 8, PL 1). In the fowl (Fig. 7, PL 1), 

 and in the sole (Fig. 9, PL 1), they are nearly 

 twice as large as in man. In the injects they 

 are also frequently of large size, as in the cock- 

 chafer (Fig. 10, PL 1). 



The proof that blood-stains have been produced 

 by human blood on articles of dress and other 

 things, is frequently important in medico-legal in- 

 vestigations. Although it cannot be distinguished 

 from all other kinds of blood, it may be from some ; 

 and the Microscope has been employed as an adjunct 

 in such cases. 



