122 T O R R E Y A 



proper fungus to grow while wash water from the other dish would be of no 

 benefit. 



To the uninitiated such results border on magic, and such small quantities 

 are meaningless. What is 0.001 of a microgram? I will try to tell you. A tea- 

 spoonful of biotin weighs about 3 grams. Take one third of it and in your 

 imagination divide it into 1000 parts. Each part would be a milligram. Take 

 one milhgram and divide it into 1000 parts. One of these is a microgram. It is 

 only necessary to think of one microgram divided into 1000 parts to obtain 

 0.001 of a microgram or one trillionth of a gram. Easy to do isn't it, in your 

 mind's eye? 



But if such a small amount cannot be seen or weighed how can it be meas- 

 ured — anywhere else, that is, than in one's imagination. This is a simple 

 laboratory procedure, based on the principle of dilution. If we dissolve 1 gram 

 of biotin in a liter of pure water it is clear that one milliliter of the solution 

 will contain 1 milligram of biotin. A milliliter can be readily and accurately 

 measured by means of a suitable pipette. If we transfer a milliliter of solution 

 containing a milligram of biotin to another flask of a liter of pure water and 

 distribute it there, then one milliliter in the second flask will contain one 

 thousandth part of a milligram, or one microgram. A third transfer of this 

 sort will yield a solution containing per milliliter 0.001 microgram or one tril- 

 lionth of a gram. To obtain such small quantities is easy, if one knows how. 



How vitamins work. Such small quantities of the vitamins are effective 

 in determining the growth of an organism, like a fungus, in comparison with 

 the amount of some other food, such as sugar or nitrogen, that our curiosity 

 as to how vitamins function is sure to be aroused. It appears that they are 

 parts of enzyme systems, and enzymes are those substances found in the body 

 which make possible the chemical changes continuously occurring in a living 

 organism and synonymous with life itself. Much as a bit of oil speeds a huge 

 machine, an enzyme makes chemical reactions go on which otherwise would 

 take place very slowly indeed. Sugar dissolved in sterile water will remain 

 unchanged indefinitely but in the presence of the proper enzyme it is broken 

 into its parts and yields its products. Alost enzymes, perhaps all, are made up of 

 two parts, an enzyme protein and a coenzyme, neither of which is effective by 

 itself. 



Some of the vitamins are known to be precursors of coenzymes. A de- 

 ficiency of one of these vitamins interferes with the activity of an enzyme 

 system and prevents the normal metabolic changes accomplished through the 

 agency of that system. For example, cocarboxylase is the pyrophosphate of 

 thiamine. The enzyme, carboxylase, catalyzes the decarboxylation of pyruvic 

 acid, one of the intermediates in the metabolism of glucose; but carboxy- 

 . lase is only effective in the presence of its coenzyme, cocarboxylase. When 



