STANDARDS FOR MEDICINES— COOK 447 



common adulterants. Another series of tests for almost all chemical 

 substances deals with the identity of the product. 



Chemicals are also frequently assayed by quantitative methods 

 to determine their percentage of purity. Sometimes tliis is a simple 

 chemical reaction such as the neutralizing of an acid with an appro- 

 priate amount of standard alkah, the indicator showing by color the 

 point of neutrality and the calculation proving the degree of purity. 

 Other assays arc much more complex but the objective is identical 

 and the tests so applied that excessive amounts of foreign substances 

 will be detected or the official quahty of the material under investiga- 

 tion verified. Frequently the ingenuity of the chemist is tried to a 

 high degree in maintaining accuracy and skill in carrying out these 

 tests. Some assays are relatively simple, as for instance in the oint- 

 ment of mercury in which the fatty vehicle is dissolved by a suitable 

 solvent, leaving the metallic mercury which can be dried and weighed 

 to determine the strength of the original ointment. 



In recent years, a new series of tests have been developed dealing 

 with the vitamin activity of cod-liver oil. Only a few years ago it 

 was demonstrated that there existed in this remarkable oil at least 

 two factors which were essential for health. A deficiency of either 

 of these in humans, and especially in children, is often the cause of 

 serious physical defects. The amount which is present in the oil 

 under examination is determined by feeding it in measured amounts 

 to rats which have been kept on a diet free from the vitamin under 

 test, and with the animal consequently suffering the characteristic 

 deficiency diseases. The amount necessary to restore the animal to 

 health indicates the amount of the vitamin present. The results of 

 such assays are based upon the average of a number of tests and can 

 only be decided when they have been carried out over many weeks 

 of experimentation. 



That these official tests for identity, purity, and strength may be 

 effectively carried out, by both the producer of a product and the 

 officials enforcing these standards, there is the necessity of thorough 

 training and experience for the scientist carrying out the tests. This 

 army of experts, guarding the manufacturer and his products, and 

 those supporting the activities of officers of inspection in the Federal 

 and State Governments, represent a large group of scientific experts 

 who are actively engaged in an important part of the health program. 



The members of the committee of revision serve voluntarily as a 

 contribution to the professions and to public welfare. This principle 

 of voluntary service brings about an unusual degree of cooperation 

 between the enforcement officials of the Government and the manu- 

 facturers of medicinal products and the experts in these fields asso- 

 ciated with colleges and universities. 



