lo Aug., 1912.] TJie Etiology of CoiiiagioNs Diseases. 



49T 



a large number of fine filaments or flagellse surrounding them, which, by 

 rapidly moving, are capable of producing motion in the organism ; whilst 

 later in their life history they assume a type similar to that of tetanus- 

 and go into sporulation. and in this form are difficult to eradicate from 

 the soil. There arc Aarinus t\pes and 

 forms of bacilli in which flag-llse 

 are pre.sent, such as typhoid, cholera, 

 &c. Organisms are widely d'stri- 

 buted through nature i.i the earth, 

 air, and water, and nearly all differ 

 .somewhat from others in their food 

 requirements ; also in the temperature 

 in which they will both live and 

 thrive. Those which are d'sease pro- 

 ducing, or pathogenic — for it must be 

 understood that not all are harmful 

 — grow most rapidK at about the 

 temperature nf the human body. 

 That they are capal)le of livi ig under 

 a wide variety of circumstances, how- 

 ever, is shown by the fact already 

 mentioned in respect of anthrax. 

 Germs rriay gain access to the svstem 

 in various ways through the alimen- 

 tary canal, lungs, skin, mucus mem- 

 lirane. &c.. but they are not capable 

 of producing any harmful effect un- 

 less there is a predisposi'.ion on the 

 part of the animal to suffer from the 

 products of the organism introduced 

 — as, for example, swine fever in 

 pigs, blackleg in cattle. As factors of their power to do harm, the chan- 

 nel by which they are introduced must be considered, as many of thertx 

 grow only in certain tissues. The physical condition of the part and the 

 miinl'T (if cr-nnisms introduced havf also to be considered, whilst, for 



ever fighting against the in- 

 troduction of organisms intc* 

 th.^- s\stem, there are the 

 white cells of the blooc! 

 (Fig. 5). These have the; 

 power of seizing and prac^ 

 tically digesting within them- 

 selves nearly all clashes o£ 

 organ'sms. The process i& 

 known as phagocytosis. 

 Should the vitality of the 

 animal be lowered, or the 

 organisms introduced in ex.- 

 FiG. 6. TEST TLKKs WITH cuLTURtis. ^essive numbers, this power 



. . is not sufficient to chect 



them m then- progress, and the result is that disease develops. As has 

 already been .stated, organi.sms are extrem.elv small bodies; so .small that 

 •special methods have to be adopted in order to recognise them. In the 

 t.rst place, special staining is necessary in order to display their fomi. 



Ml 



FIG. 5. PH.4GOCVTOSIS SHOWING 



DESTRUCTION OF ANTHRAX BACILLI 



BY WHITE CELLS OF BLOOD. 



