data <- scan(what = list(treatment="",period=0,subject=0,conc2hrs=0,conc12hrs=0), multi.line=F)
            300cap        1         1     0.667               0.200
            300cap        1        10     0.700               0.333
            300cap        1        11     0.667               0.233
            300cap        2         3     0.733               0.200
            300cap        2         5     0.667               0.167
            300cap        2         7     0.733               0.200
            250cap        1         4     0.680               0.280
            250cap        1         7     0.800               0.320
            250cap        1         8     0.800               0.320
            250cap        2         1     0.480               0.160
            250cap        2         6     0.680               0.200
            250cap        2        12     0.720               0.160
             450dr        1         3     0.156               0.156
             450dr        1         9     0.111               0.111
             450dr        1        12     0.133               0.244
             450dr        2         2     0.133               0.178
             450dr        2         4     0.156               0.178
             450dr        2        11     0.200               0.178
            300sol        1         2     0.700               0.267
            300sol        1         5     0.733               0.333
            300sol        1         6     0.600               0.233
            300sol        2         8     0.700               0.200
            300sol        2         9     0.567               0.133
            300sol        2        10     0.567               0.200

data

lithium <- data.frame(data)
rm(data)

lithium$period <- as.factor(lithium$period)
lithium$subject <- as.factor(lithium$subject)
lithium$treatment <- as.factor(lithium$treatment)

 # intrablock analysis

lithium.lm  <- lm(conc12hrs ~ period +subject +treatment, data=lithium)

anova(lithium.lm)

 # check assumptions 

par(mfrow=c(2,2))  
plot(lithium.lm)
par(mfrow=c(1,1))