ACKKOWIiEDGME^^^T. 
As this standard is based upon the one established by Ehrlich, the 
principles involved and the methods employed are practicall}^ a repro- 
duction of his work. First of all, I have to acknowledge not only the 
debt I individually owe, but the debt that all the world owes, to the 
remarkable genius of Ehrlich, who has done more, perhaps, to forward 
the problems of serum therapy than anyone else, not excepting 
Behring and Roux, the discoverers of the practical uses of diphtheria 
antitoxin. It is therefore evident that in the following pages no 
claim to originality can be made. In a few instances some improve- 
ments in the methods of testing, leading to increased accuracy, have 
been introduced. I have naturally drawn heavil}" upon the published 
literature on the subject, particularly the writings of Ehrlich, also 
Morgenroth, von Dungern, Madsen, Arrhenius, Marx, Smith, and 
Welch. 
A bibliography of all the articles consulted in writing this bulletin, 
as well as in the work of standardizing the serum, will be found 
on page 85. 
It is a pleasure to acknowledge particularly the assistance I have 
had from my colleague. Dr. Reid Hunt, Chief of the Division of Phar- 
macology, whose deep insight into physiological chemistiy has helped 
me to a better understanding of some of the problems involved in 
making the immunity unit. 
I also wish to acknowledge the assistance especially of Passed 
Assistant Surgeons John F. Anderson, the assistant director in this 
laboratory, and also Passed Assistant Surgeon R. von Ezdorf, and 
T. B. McClintic, and Assistant Surgeons Edward Francis and A. M. 
Stimson, who have faithfully carried out many details of the work 
under my supervision. 
The inception of the law and the benefits that have already resulted 
from its administration are properly credited to the Surgeon-General 
of the Public Health and Marine-Hospital Service. It is therefore 
a pleasant duty to acknowledge this as one of the many debts our 
country owes to the public health work of Walter Wyman. 
(5) • 
