The Wonders of Microscopy 309 



dimensions of the very minute red blood corpuscles differ in dif- 

 ferent mammals, and the circular shape in all mammals (except 

 camels) can be distinguished at a glance from the elliptical shape 

 in all the other backboned animals. Moreover, the red blood pig- 

 ment of haemoglobin can be easily made to assume a crystalline 

 form, and it is a very remarkable fact that the blood-crystals of 

 the horse can be distinguished microscopically from those of the 

 ass, and even those of the domestic dog from those of the wild 

 Australian dingo. Poisons that crystallise may also be detected 

 by means of the microscope. 



The use of the microscope in medicine may be illustrated in 

 reference to the blood. For it is often possible by microscopically 

 examining a film of blood, spread on a slide, to tell what is wrong 

 with the patient. Microscopic parasites may be detected, like 

 those of malaria; methods of counting the red blood corpuscles 

 (man has trillions!) may show that they are far below the proper 

 number; and a change in the normal shape of the hemoglobin 

 crystals may show that something is amiss. It is unnecessary to 

 dwell on the medical importance of the microscope in determining 

 the presence or absence of certain kinds of microbes and higher 

 parasites in the blood or food-canal of the patient. Along with 

 this physiological utilisation of the microscope we may take its 

 use in testing drinking water, which is liable to be fouled by the 

 presence of bacteria and various minute animals. Also of great 

 importance is the microscopic study of milk, for this fluid is 

 peculiarly liable to contamination, and is very suitable for the 

 growth of various kinds of disease germs. 



For the detection of adulteration the microscope is also in- 

 valuable. The starch grains of different plants, such as potato, 

 wheat, rice, maize, are readily distinguished from one another, 

 and a microscopic examination may immediately prove that a 

 commodity sold under a particular name, e.g. as arrowroot, is not 

 what it professes to be. If a sample of so-called "honey" contains 

 no pollen-grains, but a great many starch-grains, we may be sure 



