140 



SCIENCE-GOSSIP. 



from which such a sample be drawn. For instance, 

 a cubic yard of air taken from a mountain peak 

 will contain an average of about one germ ; an 

 equal quantity of air from mid-Atlantic will con- 

 tain six ; from a city park, 450 ; from a city street, 

 4,000 ; from an inhabited room, 10,000 : the 

 dustiest spots showing the highest averages. At a 

 a moderate computation a man in the course of his 

 three-score years and ten will inspire twenty-five 

 millions bacteria, which is about the number he 

 would obtain from half a pint of fresh milk. Just 

 as no atmosphere is free from dust (i) so no atmos- 

 phere is free from germs ; so that the long-cherished 

 belief that they could spring from nothing and 

 come from nowhere is not as absurd as might at 

 first sight appear. 



We will now consider the structure, mode of 

 growth and development of these creatures. Each 

 microbe is a distinct individual, a tiny cell, 

 averaging perhaps xs^iut of an inch in length, 

 and TJ3-J00 inch in breadth, or, to put it more 

 graphically, of such a size that 400,000,000 of them 

 could find standing room on a postage-stamp. The 

 smallest known bacillus is that of influenza, but 

 recent researches in connection with foot and 

 mouth disease point to the existence of germs so 

 small as not to be revealed by the modern micro- 

 scope. Yet even in these infinitesimal bodies a 

 distinct plan and structure is detectable. There is 

 a soft central portion covered by a thick outer 

 layer or skin. The outer covering may be trans- 

 parent or pigmented, or may be pitted or furnished 

 with long waving processes like those of an 

 octopus. 



There is an infinite variety in the world of germs, 

 no two species being exactly alike as regards shape, 

 size, or methods of movement and multiplication. 

 In shape they may be rounded spheres, like billiard 

 balls, short straight rods like pencils, or curved, 

 corkscrew, or comma-shaped bodies. Forms re- 

 sembling clubs or dumbells are not uncommon. 

 If when swimming freely these are observed under 

 the microscope some species 'will be seen to be 

 stationary, others to spin round like a top, to 

 gently oscillate, to slowly travel in a tortuous 

 serpentine manner, or to dash across the field like 

 an express train. As far as is at present known 

 they have neither legs, wings, nor fins, so that the 

 mechanism of their movement is a complete 

 mystery. Some observers have thought that the 

 long waving cilia, or fringe-like processes, were the 

 means employed, but these are not present in 

 many moving forms. Some of my readers may 

 know that the same mystery surrounds the move- 

 ment of some of the higher forms of life, such as 

 the diatoms. 



If a germ be watched under favourable circum- 



(1) "Dust," by J. O. Symes, M.D. Science-Gossip, N.S. 

 vol. iv. p. 100. 



stances, it may be seen to elongate into twice its 

 original length, break suddenly in the middle and 

 become two distinct individuals. Others may be 

 seen throwing out buds, which soon become 

 detached from the parent cells and swim off 

 to lead an independent existence ; or, again, an 

 apparently quiescent organism will be seen to split 

 into halves or quarters, and these again to further 

 subdivide. So rapid is their increase that a single 

 microbe may become 16,000,000 in twenty-four 

 hours, the method of procedure being as follows : 

 a germ, we will say, can produce two of its kind in 

 an hour. During the second hour there are conse- 

 quently four; during the third, eight, and so on, 

 until at the end of three days the original microbe 

 has, it is calculated, become 4,772 billions, weighing 

 some 8,000 tons. Fortunately for ourselves these 

 micro-organisms are tender plants, and unless 

 put under the most favourable conditions cannot 

 increase at anything like the rate referred to. 

 To obtain its maximum growth, each species 

 requires a peculiar temperature, a certain degree 

 of moisture and a particular food. Thus many 

 die by the way — victims to cold, starvation and 

 exposure. Direct sunlight and a constant current 

 of fresh air prohibit the growth of many kinds of 

 bacteria. This is especially true of disease germs, 

 and affords an explanation of the fact that darkness, 

 dirt and a foul atmosphere are the invariable 

 characteristics of an unhealthy house or locality. 

 There are still other dangers that the germ has 

 to grapple with. Like animals of larger size they 

 prey upon one another, and in a limited space 

 crowded with several species the weakest soon go 

 to the wall. Certain species too are guilty of a 

 form of suicide, the chemical products that they 

 manufacture finally killing them ; or, if we like 

 to look at it in another way, their life-work com- 

 pleted they choose to depart. For instance, the 

 yeast-germ that converts malt and sugar into 

 alcohol is killed when the alcohol reaches a certain 

 strength. These are, therefore, the first victims 

 to drink ! Many microscopic forms of animal life, 

 with which our rivers, Soil and air abound, live 

 upon bacteria, and, speaking generally, there are a 

 thousand and one agencies at work keeping their 

 numbers within reasonable limits. 



In order to prevent their absolute extinction 

 certain means of protection have been provided by 

 nature. This protective measure is known as 

 "sporing." The oppressed and hunted bacillus 

 can, as a last resort, alter its original shape, 

 become spherical, and throw out around itself 

 a horny covering. Within this it can defy for 

 considerable periods of time the extremes of heat 

 cr cold — boiling and freezing. Damp or drought, 

 starvation or plenty, now make no diflerence. 

 The organism for a time has ceased to be a 

 bacillus and becomes a " spoi-e," a condition 



