184 



♦ KNOW^LEDGE ♦ 



[July 1, 1889. 



body there are no bacteria, except in tte alimentary canal 

 and upper respiratory passages. It must not be supposed 

 that all bacteria are the forerunners of disease ; such is the 

 case with only certain forms to which the significant term 

 Pathotjenic hacteria is applied. Many authorities assert 

 that the non-pathogenic forms may, under certain circum- 

 stances, develop into pathogenic forms. This, however, has 

 not been definitely settled, since we are only able to separate 

 the different classes of bacteria by their action on culti- 

 vating media and on the living body. We have not yet 

 been able to develop by cultivation a virulent form from 

 a non-virulent, although we have by repeated cultivation 

 diminished the virulence of some of the most malignant 

 bacteria. 



Of all the rathogenic hacteria we have the most direful 

 tale to tell. Of one discovered by Dr. R. Koch — namely, that 

 of tubercle — the tsrrible ravages on human life by ferocious 

 animals in India (over 2i,800 fatalities per annum) are but 

 trifling compared to the ravages stealthily done in our 

 midst by this the smallest of the class of most minute 

 living units. According to Dr. Koch's estimate one-seventh 

 of the human race die of pulmonary consumption, and this 

 is only one, certainly the most prolific, of the many disease.s 

 directly caused by the tubercle bacillus. 



Happily for warm-blooded animals, these terrible death- 

 dealers diflerfrom most other bacteria, for although they can 

 remain alive for some time outside the body, they are unable 

 to develop in the outside world, and this considerably 

 limits their number. A temperature above 96° Fahr. is 

 necessarj- for their growth, and there are only a very few 

 soils on which they can be cultivated, such as blood-serum 

 and meat jelly. Moreover, they develop more slowly than 

 other known bacteria, which may consequently outgrow 

 them, and prevent their development. How, then, are we 

 to account for the ftict that tubercle is such a widely-spread 

 disease, not only among all the races of men, but also among 

 many of the lower animals? The consider.ation of the 

 following facts answers this question. 



The tubercle bacillus can form resting spores ; con- 

 sequently when once the tissues of a part have their vitality 

 80 lowered that the entrance of the bacilli is allowed, they 

 can retain their hold with great tenacity. Although the 

 bacilli cannot develoj] outside the body, their vitality is 

 preserved for a long time ; they have been found active in 

 dried sputum as many as 180 days old. The sputum of 

 consumptive patients swarms with bacilli, and great care- 

 lessness is often evinced in dealing with this. Certain 

 animal products used for food, such as the milk of tuber- 

 cular cows, contain the bacilli. Experiments, such as 

 causing animals to inhale the tubercle bacilli, or the intro- 

 duction of them into the blood, or sometimes the feeding on 

 tubercular matter, result in tuberculosis. 



Pulmonary consumption presents an example of the most 

 typical way in which the tubercle bacillus peiforms its 

 deadly work. In the majority of cases the bacilli are 

 inhaled with the air, but may also infect the lungs by the 

 blood carrying tliem from tuberculosis in other parts of the 

 body. The bacilli are incapable of independent movement. 

 This difficulty is too readily overcome in the body, as the 

 streams of blood and lymph easily carry them along. 



Their movement in the body may be .aided bj' certain 

 scavengers that are crawling about in our tissues and 

 circulating in our blood, namely, the wandering cells of con- 

 nective tissue and the white blood corpuscles. These take 

 up the bacilli by wrapping their substance around them ; 

 then for a time they crawl about carrying with them the 

 bacilli. In this attempt to devour the tubercle bacillus they 

 often find they have cavight a Tartar, who in turn feeds on and 

 multiplies in them, and thus their wandering days soon end. 



The bacilli .and their secretions causa great irritation in 

 the cells containing them, and also to the tissues around ; as 

 a result of this a most erratic growth of cells occurs, which 

 pushes aside and causes atrophy of the normal tissues, thus 

 forming a tubercle nodule. 151ood-ves3cls do not form in 

 the nodule ; the central cells, deprived of their nutriment, 

 and irritated by the secretions of the bacilli, die and co- 

 agulate into a cheesy mass, whilst at the periphery of the 

 nodule the growth continues, and may join other nodules. 

 In the cheesy centre the bacilli remain for a while, and their 

 spores, when present, for a much longer time. 



By-and-by one of these nodules may become softened, and 

 work its way into an air passage, and the mass of tissue 

 may be either coughed up or be drawn down as a fresh focus 

 of mischief to other parts of the lung. As a result of this, 

 if the nodule be large, a cavity is formed, which increases in 

 size and joins other cavities. Blood-vessels may be broken 

 into, causing bleeding and gener.il infection of the system. 



In this way a fatal state of affairs is brought about. 



TuVjeroulosis may infect all parts and organs of the body, 

 the process varying somewhat with the structure of the 

 organ affected. 



Many other diseases are also known to be caused by 

 bacteria, such as anthi-ax, cholera, pneumonia, typhoid fever, 

 erysipelas, leprosy, suppuration, and ordinary blood-poison- 

 ing. Before Sir Joseph Lister introduced the system of 

 antiseptic surgery, bacteria were a most fertile source of 

 danger in surgical operations by the decomposition and sup- 

 puration they set up in the wounds. 



In this short paper it is impossible to describe the 

 characteristics of any other pathogenic bacteria, but perhaps 

 enough has been written to show the great danger to which 

 we are exposed from attacks by an immense army of minute 

 foes. Our defences against these will be the subject of 

 another paper. 



ON EARTH-WORMS. 



Bv E. Mansel Sympson, M.A., M.B., Cantab. 



1— ^^^^^S]ET us start by tracing the young eai'th- 

 STsl^Siw worm from its egg to adult life, we shall 

 then see the relations of the stages 

 through which it passes to other forms of 

 animal life, and we shall get clearer ideas of 

 the several parts and organs of the adult 

 earth-worm. At starting, like everything 

 else in the animal and indeed vegetable 

 kingdom, the fertilised egg of the earth-worm is a mere tiny 

 mass of jelly-like protoplasm — a peculiar compound of 

 carbon, h3'drogen, oxygen, and nitrogen, which has never 

 yet been obtained save as a product of living bodies, and 

 which forms the basis whence all organs, nay all cells, in 

 the living world have sprung. This mass of protoplasm is 

 called a cell, and has a smaller mass of .somewhat altered 

 protoplasm and nucleus inside it. It is laid in a case or 

 cocoon, of somewhat the same structure as a beetle's w-ing, 

 which has probably been secreted by a large gland in the 

 upper end of the earth-worm's body. Soon the one cell 

 begins to divide inta two, and the.=e into four, and so on, 

 till, eventually, what was the egg-cell consists of a great 

 number of cells, all, however, just alike. In the next stage 

 these cells become arranged in two rows or layers, 

 and all of those in one layer are larger than those 

 in the other. The little animal so formed becomes con- 

 cave, hollowed out on the side formed by the larger 

 cells, until it assumes the form of a sac, with an 

 opening — the future mouth — at one end, the cavity 

 of the sac being the primitive alimentary canal, lined 



