Abstract
Colorimeters and non-recording spectrophotometers for visible and ultra-violet light have been used for many years and are to be found in most microbiological laboratories. With the need for greater speed of operation, recording instruments are now coming into more general use. During the last two decades recording infra-red spectrophotometers have been developed and these have enabled the absorption measurements on micro-organisms to be extended into the infra-red region of the spectrum. Two factors have tended to retard the use of infra-red spectrophotometry. One is the high initial cost of the equipment and the other is the large absorption of infra-red radiation by water. Despite these difficulties, a considerable amount of work has now been done and it seems profitable to review the varied applications to which infra-red spectroscopy has already been put and to indicate the results which have been obtained by its use.