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D. E. SALMON. 
located is a close one, that he is able to live in an atmosphere that 
would immediately place the dog hors de combat. We must also 
assume that the dog, even in this partially asphyxiated condition, 
continues to live and exhales a poison which would gradually 
accumulate and overcome the man unless its production was so 
slow that the man would become inured to it before it had been 
produced in sufficient quantities to overpower him. In the former 
case we might suppose that the slight ventilation of the room and 
the smaller amount of oxygen used by the man would in time 
place the dog in a condition to make an attack. And here, after 
all our attempts to make the conditions parallel, we fail miserably, 
for the dog's attack must be essentially a physical one, while the 
microbe’s attack partakes but slightly, if at all, of that character. 
Of what use, then, is such a comparison for the elucidation of 
this nature ? Surely any conclusions drawn from it must be un¬ 
safe, misleading, or diametrically opposed to the truth. 
“ It is evident,” says the learned doctor, “ that we can substi¬ 
tute nitrogen or bile in the place of the oxygen of this problem, 
and do no violence to the sense or the results.” Here, again, the 
conclusion seems to be most hasty and without that consideration 
which we should expect in discussing a question of this importance. 
A moment’s thought would have convinced our able critic that, 
if the multiplication of microbes is to be prevented by withdrawing 
an element from the liquid in which they exist, it is a necessary 
condition of the case that the element should be one essential to 
the growth and multiplication of the germs. As a matter of fact, 
neither free nitrogen nor bile is essential to such growth and 
multiplication. The germs of various contagious diseases can be 
and have been cultivated where neither nitrogen nor bile exists; 
but all microbes that have been carefully studied and which pro¬ 
duce diseases that are followed by immunity, so far as I have 
been able to learn, require a certain amount of free oxygen. 
Finally we are told: “Dr. Salmon admits the solution of the 
question by natural selection when he says the ‘ recovery is due to 
the ability of the cells to resist the poison.’ Immunity is also 
due to the same fact. The oxygen theory is, therefore, only a 
rider to the true solution—very much such a rider, too, as Mazeppa 
