The idea is current among both pharmacologists and clinicians that substances which are readily soluble in water are also readily absorbable from the gastrointestinal canal, except when some physical law, such as that of osmosis, interferes with the absorption. Thus a prominent pharmacologist, speaking of a drug which requires 950 parts of water for its solution, says, "It is evident, however, that a substance which is so sparingly soluble as this must go into solution in the intestine with great slowness, and, therefore, linger in the bowel for a considerable length of time."
A second belief, current more particularly among clinicians, and also held by many pharmacologists, is that there exists a fairly constant ratio between the dose of a drug by subcutaneous administration and that by mouth or rectum, or between the latter two. Cushny1 says:
As absorption from the subcutaneous tissues is so much more rapid than
HATCHER RA, EGGLESTON C. STUDIES ON THE ABSORPTION OF DRUGS. JAMA. 1914;LXIII(6):469-473. doi:10.1001/jama.1914.02570060029009