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1883,} 89 [Lockington. 
During the last few years the microscope has been largely employed in 
the investigation of diseased tissues, especially in cases of those diseases 
called ‘‘zymotic;’? and the result of this examination has been to show 
that certain specific forms of disease are invariably accompanied by what 
appear to be specific types of microbes—or at any rite by types that are 
constant in their relation to the disorder they accompany. 
In this way Pasteur has made us acquainted with the parasite which ac- 
companies anthrax, charbon, or malignant pustule, and with some others, 
Laveran has described and figured that of malaria, and Koch has shown 
that consumption has also its parasitic companion. 
So generally have special forms been found associated with special dis- 
eases, and so invariably have these special forms been found to increase in 
number of individuals as the disease with which they are associated has 
increased in severity, that a large proportion of scientific and medical men 
have arrived at the conclusions that every inflammatory disease (if not 
every disease) has its specific parasite ; and that the parasite is the cause of 
the disease. 
This explanation certainly lies upon the face of the facts, but a little 
consideration will show that neither the specdfic nature of the parasite, nor 
its direct causation of the disease, are proved by any series of observations 
yet on record. 
Observations upon the higher animals have conclusively proved that 
they are subject to considerable changes caused by their environment. 
Within the limits of a single so-called species occur so many variations 
that the definition of a species has become difficult. Besides those varia- 
tions due to sex and to age; individual, racial, and ‘varietal differences 
occur, to such an extent as to render the systematic arrangement of living 
forms a most bewildering task, and one respecting which no two biologists 
agree, 
These variations right and left of the average of a species are admitted 
on all hands to be produced by natural forces, organic and inorganic, by 
gravity, heat, cold, moisture or drouth, plenty or lack of food, confine- 
ment or freedom, cultivation (which is an environment of man’s making) 
or heredity, which is the effect of the continued environment of ancestors. 
No man can look dispassionately at his own physical and mental condi- 
tion without acknowledging that, leaving heredity aside, he is what he is 
On account of what he has experienced. . 
The changes of cell-structure which take place in the arm of a man who 
abandons the yard-measure for the blacksmith’s hammer would, could 
they be examined with the microscope in the same way that we ean watch 
the changes of an amcba, be seen to be a thousand-fold greater and more 
complicated than those of that rhizopod, 
As instances of what a change of environment can do in creatures built 
Up of many thousand cells, each cell as complex as is the entirety of the 
parasitic organisms we are inquiring into, the foilowing will suftice : The 
PROC, AMER. PHILOS. 800. XXI, 114. L. PRINTED JUNE 22, 1883. 
