METHODS OF INVESTIGATION 25 



to contain a pressor substance. All other organs and tissues, 

 but especially nervous tissues, contain a depressor substance, 

 or depressor substances (see Figs. 1-8). 



The subject of intravenous injection of tissue extracts has 

 played such a large part in connection with internal secretion 

 that it must be dealt with in some detail. Considerable 

 naivete has been displayed by many observers, both as to 

 details of method and as to the interpretation of the results 

 obtained. Thus, for example, it has too often been assumed 

 that a slight rise or fall of the blood-pressure obtained after 

 injection of a fluid into the circulation is in reality due to some 

 specific action of the extract, and not due, as it very likely is, 

 to its effects qua fluid, or to its temperature, or to the rate of 

 injection, or to some other adventitious circumstance. Again, 

 it has been rashly concluded in many cases that because an 

 extract of a certain tissue or organ produces a certain effect, 

 for example, on the blood-pressure, that this is evidence of an 

 internal secretion on the part of the tissue or organ in question. 

 This unjustifiable attitude is being continually maintained. 

 Thus, Livon divides the glands of the body into two groups, 

 "hypertensive" and " hypotensive," according as their 

 extracts when injected into the circulation of an animal cause 

 a rise or a fall of the blood-pressure. The adrenals, the 

 pituitary, the spleen, the kidney, 1 and the parotid, are placed 

 in the former group ; the liver, lung, pancreas, thymus, ovary, 

 and testis in the latter. 



As we have seen, the remarkable discovery of Oliver and 

 Schafer stimulated numerous observations upon the special 

 physiological effects of extracts made from different organs 

 and tissues. These authors noted, in addition to the effects 

 of adrenal extracts, that pituitary preparations also produce 

 a rise of blood-pressure. And we may state at the present 

 time, with some degree of certainty, that these are the only 

 two tissues in the body an extract of which produces pressor 

 effects. 



Professor Schafer also, working in conjunction with the 

 present writer, found that a depressor substance is also present 

 in pituitary extracts, and noted " a certain similarity of physio- 



1 It is doubtful in any case whether the spleen and kidney would be in- 

 cluded in the pressor group. (In regard to the kidney, see p. 52.) 



