In Roux’s apparatus, made by Lequeux, the make and break is attained by the movement of one limb of a bimetallic thermostat, and in some forms a resistance coil and rheostat are placed in the circuit.
At the Pasteur Institute in Paris, and at other large laboratories in France, the bacteriological incubator is raised to the dimensions of a room. In the centre of this room is a large boiler heated by gas-burners, the fumes from which pass through a large flue to the outside. The flame of the burners is regulated by a bimetallic thermostat. The gas by-pass can be regulated by an attendant. The cultures are contained in vessels placed on shelves, which are ranged round the side of the room.
Human Incubators.
| Fig. 13.—Tarnier’s Incubator. |
The first incubator designed for rearing children who are too weak to survive under normal conditions, or who are prematurely born, is that of Dr Tarnier. It was constructed in 1880 and was first used at the Paris Maternity Hospital. Its form is that of a rectangular box measuring 65 × 30 × 50 centimetres (fig. 13). It is divided into an upper and lower chamber; the former contains the infant, while the latter serves as a heating chamber, and in reality is simply a modified water-tank. The partition (P) which divides the incubator into two chambers does not extend the whole length of it, so that the upper and lower chambers are at one end of the apparatus in communication with each other. It is through this passage that the heated air from the lower chamber passes into the upper one containing the infant. The narrow bottom chamber C serves to prevent loss of heat from the base of the water-bottles. The outside air is admitted into the lower chamber at the opposite end, through an aperture (A), and passing over a series of bottles (B) containing warm water, becomes heated. The air is rendered adequately moist by means of a wetted sponge (S) which is placed at the entrance of the lower chamber into the upper. The warmed and moistened air is determined in its direction by the position of the outlet aperture (O), which is situated above and just behind the head of the infant. It contains a helix valve (H) and the rotation of this is an indication that the air is circulating within the incubator.
The child is kept under observation by means of a sliding glass door (G) situated in the upper or roof wall of the incubator. Immediately beneath this, and attached to one of the side walls, is a thermometer (T) which records the temperature of the air in the infant-chamber. The temperature should be maintained at 31° to 32° C. The precise limit of temperature must of course be determined by the condition of the child; the smaller and weaker it is, the higher the temperature must be.
The warm water vessels contain three-quarters of a pint of water and four of them are sufficient to maintain the required temperature, provided that the external air does not fall below 16° C. The vessels are withdrawn and replaced through an entrance to the lower chamber, and which can be opened or closed by a sliding door (D).
The walls of the incubator, with the exception of the glass sliding door, are made of wood 25 millimetres thick.
The apparatus appears to have been successful, if by success is understood the indiscriminate saving of life apart from all other considerations, since the mortality of infants under 2000 grammes has been reduced by about 30%, and about 45% of children who are prematurely born are saved.
Dr Tarnier’s apparatus requires constant attention, and the water in the warm water vessels needs renewing sufficiently often. It is not provided with a temperature regulator and consequently fluctuations of internal temperature, due to external thermal variations, are liable to occur.