198 



MODERN HORSE MANAGEMENT 



[CHAP. 



777. We will now briefly consider the various 

 forms of micro-organisms : 



Animal, called protozoa. 



Vegetable : bacteria, yeast and moulds or 

 fungi. 



Bacteria are divided into : (a) bacilli, or 

 rod-shaped (as those of tuberculosis, anthrax, 

 tetanus) ; {b) cocci, little spheres, which are of 

 different forms, diplococci (as in pneumonia), 

 tetracocci, sarcinse, staphylococci (as in abscesses) 

 and streptococci (as in abscesses) ; and (c) 

 spirilla, or spirals (as in syphilis). 



Bacteria, etc., are able to reproduce asexually, 

 i.e. without different sexes having to unite, very 

 quickly by merely increasing in size, and then 

 dividing into two. The rod-shaped bacillus of 

 tuberculosis divides into two rods in half an 

 hour under favourable conditions ; thus, if we 

 start with one bacillus, and place it on a suitable 

 medium, as broth, in one hour there would be 

 four bacilli, and in 32 hours there would be 

 approximately 10,000,000,000,CX)0,000,000,000,000 

 bacilli, providing that each microbe formed into 

 two at the end of half an hour ; but, fortunately, 

 such an occurrence would be most improbable. 

 Some bacteria multiply in five minutes. 



778. The study of bacteria is generally looked 

 upon as an easy task. Many imagine that all one 

 has to do is to take a high-power microscope and 

 place some infected matter under it, and then 

 to view at leisure the thousands of microbes 

 wriggling about under the lens. Such is not the 

 case, and far from it. The difficulties that beset 

 the bacteriologist are countless, and it has truly 

 been stated that there is no science with greater 

 difficulties to overcome. 



Briefly, bacteria, etc., are studied in the 

 following way: an infected substance is taken 

 and diluted considerably with freshly sterilised 

 distilled water (all vessels used must be pre- 

 viously sterilised) ; then various aniline stains 

 are used upon this infected solution, thereby 

 staining different bacteria different colours. After 

 years of study it has been discovered that various 

 bacteria "take" various stains, and thus, by 

 repeated staining and unstaining, we can eventu- 

 ally produce a certain stain in one form of 

 bacteria (the form that we suspect is present in 

 the solution) that will stand out distinct from 

 all others. In this way we can ascertain not only 

 f that particular form is present, but can study 

 it after we have found it. The presence of some 

 bacteria is detected by the actions they have on 

 different sugars. 



Again, we might have a certain matter that 

 was suspected of containing bacteria. What we 

 have to do then is to cultivate the growth, i.e. 

 produce a culture. We take the suspected matter 

 and put it into a suitable medium, such as broth, 

 blood serum, agar, gelatine, potato, milk, starch, 

 jelly, etc., and keep the whole free from atmo- 

 spheric impurities at a certain temperature for 



a day or so. At the end of this time we shall 

 find that large colonies, many visible to the 

 naked eye, have been formed, and we are then 

 able to study these colonies either as a whole or 

 by making dilute solutions of them. 



If we place a dilute solution of the original 

 matter into a thick solution of gelatine, for in- 

 stance, and form a culture, we shall find that 

 each individual bacterium, etc., has formed its 

 own gigantic culture, without being able to move 

 on account of the stiffness of the medium. Thus 

 we can take these cultures separately and 

 examine each one, by diluting it several hundred 

 times and then staining it, and find what par- 

 ticular bacteria each culture consists of. The 

 reason of the dilution to such an extent is that, 

 unless the solution is diluted to a required 

 amount, it will be impossible to see anything 

 through the microscope that will furnish us with 

 the information required. 



779. Methods of Admission into the System. 

 Pathogenic microbes enter the system in 

 various ways through the respiratory tract, the 

 alimentary canal (from mouth to anus), the 

 genital organs, the mucous membrane of the eye, 

 the navel (umbilicus), abrased skin, and any 

 form of wound or bruise. 



The virulence and even the pathogenicity of 

 a microbe often depend on the manner in which 

 it enters the system ; thus the bacterium of 

 Asiatic cholera is far more dangerous if eaten 

 than if injected under the skin, whilst, on the 

 other hand, the typhoid bacillus can be fed to a 

 rabbit without doing any harm, but if injected 

 under the skin is nearly always fatal. It must 

 be remembered that anything in the stomach or 

 intestines is as much outside of the system as if 

 held in the hand, because it must be absorbed 

 through the intestinal walls before it is in the 

 system ; thus many of the harmful germs that 

 we eat never gain access to the system. As stated 

 above, the health of the animal governs so much 

 the likeliness of any eaten bacteria doing any 

 harm. 



780. How Pathogenic Microbes Produce 

 Disease. We now come to the important ques- 

 tion of how these various pathogenic animal 

 and vegetable microbes produce disease. 

 There are several ways in which disease is 

 produced. 



Briefly they are as follows : (a) by forming 

 chemical poisons (toxins) and emptying this into 

 the blood ; (ft) by moving in the blood and form- 

 ing poisons ; (c) by destroying cells of the tissue 

 without producing free toxin in the blood ; (d) 

 by destroying the blood corpuscles. 



Protozoa (animal microbes) produce diseases 

 mostly by entering the blood and destroying the 

 red corpuscles. Such diseases as malarial fever 

 (see Sec. 640), sleeping sickness, Texas fever in 

 cattle, maladie du colt in horses, surra in sheep, 

 etc., are examples of those produced by protozoa. 



