PHYSIOLOGICAL RESEARCH, PHYSIOLOGICAL REASONING. 141 
3. Kreatin, constantly found in muscle, and a few others of 
less constant occurrence. 
The above consists of C, H, N,O. Taurocholic acid contains 
also S. 
The molecule in most instances is complex. 
Non-Nitrogenous Metabolites. 
These occur in small quantity, and some of them are secreted 
in an altered form. 
They include lactic and sarcolactic acid, oxalic acid, succinic 
acid, ete. 
PHYSIOLOGICAL RESEARCH AND PHYSIOLOGICAL 
REASONING. 
We propose in this chapter to examine into the methods 
employed in physiological investigation and teaching, and the 
character of conclusions arrived at by physiologists as depend- 
ent on a certain method of reasoning. 
The first step toward a legitimate conclusion in any one of 
the inductive sciences to which physiology belongs is the col- 
lection of facts which are to constitute the foundation on 
which the inference is to be based. If there be any error in 
these, a correct conclusion can not be drawn by any reliable 
logical process. On the other hand, facts may abound in thou- 
sands and yet the correct conclusion never be reached, because 
the method of interpretation is faulty, which is equivalent to 
saying that the process of inference is either incomplete or in- 
correct. The conclusions of the ancients in regard to nature 
were usually faulty from errors in both these directions; they 
neither had the requisite facts, nor did they correctly interpret 
those with which they were conversant. 
Let us first examine into the methods employed by modern 
physiologists, and determine in how far they are reliable. First, 
there is the method of direct observation, in which no appara- 
tus whatever or only the simplest kind is employed; thus, the 
student may count: his own respirations, feel his own heart- 
beats, count his pulse, and do a very great deal more that will 
be pointed out hereafter ; or he may examine in like manner an- 
other fellow-being or one of the lower animals. This method 
is simple, easy of application, and is that usually employed by 
the physician even at the present day, especially in private 
